Initial commit
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353
bdf/bdf.go
Normal file
353
bdf/bdf.go
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@@ -0,0 +1,353 @@
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package bdf
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import (
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"bufio"
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"encoding/hex"
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"fmt"
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"image"
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"image/color"
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"image/draw"
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"io"
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"strconv"
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)
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// glyph is a singular bitmap glyph to be used as a mask, assumed to directly
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// correspond to a rune. A zero value is also valid and drawable.
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type glyph struct {
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// Coordinates are relative to the origin, on the baseline.
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// The ascent is thus negative, unlike the usual model.
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bounds image.Rectangle
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bitmap []byte
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advance int
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}
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// ColorModel implements image.Image.
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func (g *glyph) ColorModel() color.Model { return color.Alpha16Model }
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// Bounds implements image.Image.
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func (g *glyph) Bounds() image.Rectangle { return g.bounds }
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// At implements image.Image. This is going to be somewhat slow.
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func (g *glyph) At(x, y int) color.Color {
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x -= g.bounds.Min.X
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y -= g.bounds.Min.Y
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dx, dy := g.bounds.Dx(), g.bounds.Dy()
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if x < 0 || y < 0 || x >= dx || y >= dy {
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return color.Transparent
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}
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stride, offset, bit := (dx+7)/8, x/8, byte(1<<uint(7-x%8))
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if g.bitmap[y*stride+offset]&bit == 0 {
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return color.Transparent
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}
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return color.Opaque
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}
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// -----------------------------------------------------------------------------
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// Font represents a particular bitmap font.
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type Font struct {
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Name string
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glyphs map[rune]glyph
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fallback glyph
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}
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// FindGlyph returns the best glyph to use for the given rune.
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// The returned boolean indicates whether a fallback has been used.
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func (f *Font) FindGlyph(r rune) (glyph, bool) {
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if g, ok := f.glyphs[r]; ok {
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return g, true
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}
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return f.fallback, false
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}
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// DrawString draws the specified text string onto dst horizontally along
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// the baseline starting at dp, using black color.
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func (f *Font) DrawString(dst draw.Image, dp image.Point, s string) {
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for _, r := range s {
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g, _ := f.FindGlyph(r)
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draw.DrawMask(dst, g.bounds.Add(dp),
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image.Black, image.ZP, &g, g.bounds.Min, draw.Over)
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dp.X += g.advance
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}
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}
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// BoundString measures the text's bounds when drawn along the X axis
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// for the baseline. Also returns the total advance.
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func (f *Font) BoundString(s string) (image.Rectangle, int) {
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var (
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bounds image.Rectangle
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dot image.Point
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)
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for _, r := range s {
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g, _ := f.FindGlyph(r)
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bounds = bounds.Union(g.bounds.Add(dot))
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dot.X += g.advance
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}
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return bounds, dot.X
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}
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// -----------------------------------------------------------------------------
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func latin1ToUTF8(latin1 []byte) string {
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buf := make([]rune, len(latin1))
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for i, b := range latin1 {
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buf[i] = rune(b)
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}
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return string(buf)
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}
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// tokenize splits a BDF line into tokens. Quoted strings may start anywhere
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// on the line. We only enforce that they must end somewhere.
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func tokenize(s string) (tokens []string, err error) {
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token, quotes, escape := []rune{}, false, false
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for _, r := range s {
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switch {
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case escape:
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switch r {
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case '"':
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escape = false
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token = append(token, r)
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case ' ', '\t':
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quotes, escape = false, false
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tokens = append(tokens, string(token))
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token = nil
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default:
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quotes, escape = false, false
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token = append(token, r)
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}
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case quotes:
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switch r {
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case '"':
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escape = true
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default:
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token = append(token, r)
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}
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default:
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switch r {
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case '"':
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// We could also enable quote processing on demand,
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// so that it is only turned on in properties.
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if len(tokens) < 1 || tokens[0] != "COMMENT" {
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quotes = true
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} else {
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token = append(token, r)
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}
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case ' ', '\t':
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if len(token) > 0 {
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tokens = append(tokens, string(token))
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token = nil
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}
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default:
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token = append(token, r)
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}
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}
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}
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if quotes && !escape {
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return nil, fmt.Errorf("strings may not contain newlines")
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}
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if quotes || len(token) > 0 {
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tokens = append(tokens, string(token))
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}
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return tokens, nil
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}
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// -----------------------------------------------------------------------------
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// bdfParser is a basic and rather lenient parser of
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// Bitmap Distribution Format (BDF) files.
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type bdfParser struct {
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scanner *bufio.Scanner // input reader
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line int // current line number
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tokens []string // tokens on the current line
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font *Font // glyph storage
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defaultBounds image.Rectangle
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defaultAdvance int
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defaultChar int
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}
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// readLine reads the next line and splits it into tokens.
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// Panics on error, returns false if the end of file has been reached normally.
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func (p *bdfParser) readLine() bool {
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p.line++
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if !p.scanner.Scan() {
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if err := p.scanner.Err(); err != nil {
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panic(err)
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}
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p.line--
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return false
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}
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var err error
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if p.tokens, err = tokenize(latin1ToUTF8(p.scanner.Bytes())); err != nil {
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panic(err)
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}
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// Eh, it would be nicer iteratively, this may overrun the stack.
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if len(p.tokens) == 0 {
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return p.readLine()
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}
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return true
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}
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func (p *bdfParser) readCharEncoding() int {
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if len(p.tokens) < 2 {
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panic("insufficient arguments")
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}
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if i, err := strconv.Atoi(p.tokens[1]); err != nil {
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panic(err)
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} else {
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return i // Some fonts even use -1 for things outside the encoding.
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}
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}
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func (p *bdfParser) parseProperties() {
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// The wording in the specification suggests that the argument
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// with the number of properties to follow isn't reliable.
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for p.readLine() && p.tokens[0] != "ENDPROPERTIES" {
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switch p.tokens[0] {
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case "DEFAULT_CHAR":
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p.defaultChar = p.readCharEncoding()
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}
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}
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}
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// XXX: Ignoring vertical advance since we only expect purely horizontal fonts.
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func (p *bdfParser) readDwidth() int {
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if len(p.tokens) < 2 {
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panic("insufficient arguments")
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}
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if i, err := strconv.Atoi(p.tokens[1]); err != nil {
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panic(err)
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} else {
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return i
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}
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}
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func (p *bdfParser) readBBX() image.Rectangle {
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if len(p.tokens) < 5 {
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panic("insufficient arguments")
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}
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w, e1 := strconv.Atoi(p.tokens[1])
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h, e2 := strconv.Atoi(p.tokens[2])
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x, e3 := strconv.Atoi(p.tokens[3])
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y, e4 := strconv.Atoi(p.tokens[4])
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if e1 != nil || e2 != nil || e3 != nil || e4 != nil {
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panic("invalid arguments")
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}
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if w < 0 || h < 0 {
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panic("bounding boxes may not have negative dimensions")
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}
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return image.Rectangle{
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Min: image.Point{x, -(y + h)},
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Max: image.Point{x + w, -y},
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}
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}
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func (p *bdfParser) parseChar() {
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g := glyph{bounds: p.defaultBounds, advance: p.defaultAdvance}
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bitmap, rows, encoding := false, 0, -1
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for p.readLine() && p.tokens[0] != "ENDCHAR" {
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if bitmap {
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b, err := hex.DecodeString(p.tokens[0])
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if err != nil {
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panic(err)
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}
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if len(b) != (g.bounds.Dx()+7)/8 {
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panic("invalid bitmap data, width mismatch")
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}
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g.bitmap = append(g.bitmap, b...)
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rows++
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} else {
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switch p.tokens[0] {
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case "ENCODING":
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encoding = p.readCharEncoding()
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case "DWIDTH":
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g.advance = p.readDwidth()
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case "BBX":
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g.bounds = p.readBBX()
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case "BITMAP":
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bitmap = true
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}
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}
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}
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if rows != g.bounds.Dy() {
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panic("invalid bitmap data, height mismatch")
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}
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// XXX: We don't try to convert encodings, since we'd need x/text/encoding
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// for the conversion tables, though most fonts are at least going to use
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// supersets of ASCII. Use ISO10646-1 X11 fonts for proper Unicode support.
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if encoding >= 0 {
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p.font.glyphs[rune(encoding)] = g
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}
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if encoding == p.defaultChar {
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p.font.fallback = g
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}
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}
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// https://en.wikipedia.org/wiki/Glyph_Bitmap_Distribution_Format
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// https://www.adobe.com/content/dam/acom/en/devnet/font/pdfs/5005.BDF_Spec.pdf
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func (p *bdfParser) parse() {
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if !p.readLine() || len(p.tokens) != 2 || p.tokens[0] != "STARTFONT" {
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panic("invalid header")
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}
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if p.tokens[1] != "2.1" && p.tokens[1] != "2.2" {
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panic("unsupported version number")
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}
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for p.readLine() && p.tokens[0] != "ENDFONT" {
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switch p.tokens[0] {
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case "FONT":
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if len(p.tokens) < 2 {
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panic("insufficient arguments")
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}
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p.font.Name = p.tokens[1]
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case "FONTBOUNDINGBOX":
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// There's no guarantee that this includes all BBXs.
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p.defaultBounds = p.readBBX()
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case "METRICSSET":
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if len(p.tokens) < 2 {
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panic("insufficient arguments")
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}
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if p.tokens[1] == "1" {
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panic("purely vertical fonts are unsupported")
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}
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case "DWIDTH":
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p.defaultAdvance = p.readDwidth()
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case "STARTPROPERTIES":
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p.parseProperties()
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case "STARTCHAR":
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p.parseChar()
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}
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}
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if p.font.Name == "" {
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panic("the font file doesn't contain the font's name")
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}
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if len(p.font.glyphs) == 0 {
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panic("the font file doesn't seem to contain any glyphs")
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}
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}
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func NewFromBDF(r io.Reader) (f *Font, err error) {
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p := bdfParser{
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scanner: bufio.NewScanner(r),
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font: &Font{glyphs: make(map[rune]glyph)},
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defaultChar: -1,
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}
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defer func() {
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if r := recover(); r != nil {
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var ok bool
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if err, ok = r.(error); !ok {
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err = fmt.Errorf("%v", r)
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}
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}
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if err != nil {
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err = fmt.Errorf("line %d: %s", p.line, err)
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}
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}()
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p.parse()
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return p.font, nil
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}
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